A freezer such as air conditioner, refrigerator and car cooler includes a refrigerating cycle. A hermetic compressor or an open compressor for circulating refrigerant is incorporated in the refrigerating cycle. The hermetic compressor includes a hermetic case in which a motor and a compression machine driving by this electric motor are accommodated. Compressor refrigerant is compressed, heated to high temperature and pressurized by this compression machine and discharged into the refrigerating cycle. Some conventional hermetic compressors use CFC12 refrigerant (which will be referred to as "R12 refrigerant" hereinafter) which is one kind of chlorofluorocarbon, HCFC22 refrigerant (which will be referred to as "R22 refrigerant" hereinafter) which is one kind of hydrochlorofluorocarbon, or naphthene or paraffin mineral oil having excellent compatibility with the R12 refrigerant or R22 refrigerant.
When the R12 refrigerant is used as compressor refrigerant, chlorine atoms included in the R12 refrigerant reacts with iron atoms of metal base material to form chlorine lubricant films. The lubricant film comprising the ferric chloride has self-lubricating properties and is excellent in wear resistance and prevents contact between metals to effectively prevent the wear. In addition, since the R12 refrigerant and conventional freezer oil are nonpolar, hygroscopicity is low. Therefore, the ferric chloride layer formed on iron-based metal base material does not cause hydrolytic degradation and exists as a stable lubricant film. However, since the R12 refrigerant is extremely stable chemically in the atmosphere and there is a high possibility that the R12 refrigerant destroys the ozone layer, the R12 refrigerant is designated as a restricted chlorofluorocarbon. Further, the R22 refrigerant is also a restricted chlorofluorocarbon although it is easily decomposed in the atmosphere and it has weak power to destroy the ozone layer, since the R22 still have effect to destroy the ozone layer, it has been decided internationally that the R22 refrigerant should not be used in the feature.
Recently, hydro-fluorocarbon refrigerant (which will be referred to as "HFC refrigerant" hereinafter) which does not destroy the ozone layer is developed as alternative chlorofluorocarbon as an alternative to specified chlorofluorocarbon or designated chlorofluorocarbon. Although the ozone destroy coefficient of the HFC refrigerant is zero, since it does not have chlorine atoms, there is a problem that the self-lubricating property is inferior. Further, when the hermetic compressor is operated using the HFC refrigerant as the compressor refrigerant, if the naphthene or paraffin mineral oil is used as the freezer oil, the compatibility with the HFC refrigerant is bad. Since such mineral oil is not solved into the HFC refrigerant, oil returning property is bad, lubricating and cooling effects of sliding portions of the compressor are impaired, and there is a possibility that problem such as seizing up is caused. Further, although the HFC refrigerant does not destroy the zone layer, since global-warming coefficient is thousands of times of carbon dioxide, it can be said that the HFC refrigerant is not sufficient in terms of terrestrial environment.
Thereupon, HC refrigerant and ammonia refrigerant are proposed as refrigerant which is not harmful to environment recently. The ammonia refrigerant attacks copper such as copper wire and thus, it is difficult to use it in the hermetic compressor. It is known that the HC refrigerant does not have the abovedescribed problem of the ammonia refrigerant and has excellent characteristics as refrigerant for air conditioner. Naphthene or paraffin mineral oil is generally used as the freezer oil, but when the compatibility of combination of the HC refrigerant, the freezer oil and the sliding members is bad, the wear of the sliding members is increased. Thereupon, appropriate combination of the HC refrigerant, the freezer oil and the sliding members is necessary.
If the hermetic compressor or open compressor is driven for practical test using mineral oil, since the sliding members are worn, it is necessary to use material for the sliding members in which wear resistance is enhanced. Further, rather than naphthene or paraffin mineral oil, polyalkylene glycol (which will be referred to as "PAG oil" hereinafter), ester oil having ester linkage in molecular (which will simply be referred to as "ester oil" hereinafter), or ether oil having ether linkage in molecular (which will simply be referred to as "ether oil" hereinafter) may be used as the freezer oil in some cases, and it is necessary to provide the sliding members suitable for respective freezer oils. Thereupon, the present invention has been accomplished in view of the above circumstances, and it is an object to provide a hermetic compressor or an open compressor in which the wear resistance of sliding portions of a compressor is enhanced, stably driving for a long term period can be ensured, and HC refrigerant can be used.